CK-12-Physics - Intermediate

http://www.ck12.org Chapter 2. One-Dimensional Motion

2.4 Uniform Acceleration

Objectives

The student will:

• define and explain acceleration.

Vocabulary

• average acceleration:The change in velocity divided by the duration of the time period.


• constant acceleration:A type of motion in which the velocity of an object changes by an equal amount in
  every equal time period.

Equation

• ~a
  avg=∆~v∆t, where the arrows indicate that~aand~vare vector quantities

Introduction

In everyday life, we use “acceleration” to refer to an object getting faster and picking up greater speed. In physics,

though, we use “acceleration” to meananychange in velocity. In physics, acceleration can refer to speeding up,

slowing down, or turning. Because velocity is a vector, it has a direction. A change in direction is a change in

velocity. In a car, using the gas pedal is accelerating, but so is using the brakes or the steering wheel.

To see what a change of velocity means, it is best to represent an object’s motion with a velocity-time graph. This

is extremely useful in determining acceleration and displacement.

Average acceleration is a change in velocity, divided by a change in time. It can be calculated with this equation:

~a

avg =∆~v∆t

If the rate of change in velocity is uniform, the acceleration is uniform, as well. Note that uniform acceleration and

constant acceleration mean the same thing. We will only consider uniform acceleration unless otherwise stated.

Check Your Understanding

1. How can braking provide for both negative and positive acceleration?
   Answer:If the brakes are applied while moving to the right the acceleration is to the left and therefore negative. If
   the breaks are applied while the car is traveling to the left, the acceleration is to the right and is therefore positive.


2. How can you have a negative acceleration without braking?
   Answer:Increase your velocity to the left.